High molecular weight, water-soluble polymers produced from such monomers as acrylamide are commercially and environmentally important materials. These polymers find use as flocculants for mining operations to recover ore from slurries, water treating to remove suspended impurities etc., and also are used extensively in paper making to aid paper formation and in oil recovery industries. In the production of these polymers by polymerization of their monomers, it has become increasingly important to produce as high a molecular weight polymer as possible. It has also been evident that the production of such polymers utilizing a higher monomer solids reaction media would enable the production of more useful polymers at a more economical rate. However, the combination of high polymer solids and high molecular weight has been difficult to attain through polymer preparation by solution polymerization and viscosity problems or gel formation has presented difficulties in handling and dissolution of such polymers
The advent of emulsion polymerization solved some of these problems. U.S. Pat. No. 5,286,806 teaches a method in which water-soluble monomers are polymerized in a water-in-oil emulsion to form a water-in-oil emulsion of a water-soluble polymer. In that case, the polymer is hydrolyzed to further enhance the end-use properties of the polymer. U.S. Pat. Nos. 4,956,399; 4,956,400; 5,037,881; and 5,132,023, all of which are hereby incorporated herein by reference, disclose a further advance in the art by teaching that functionalization of a water-soluble polymer contained in a water-in-oil microemulsion could be carried out to produce high molecular weight charged polymers with advantageous flocculation performance. The use of microemulsion, as opposed to emulsions, in polymer production provided improved polymer performance properties among other benefits.
Despite the many benefits provided by emulsion and microemulsion polymers, transportation costs associated with such materials remained high and disposal of the oil and emulsifier in the emulsions posed environmental concerns as secondary pollution. Moreover, many emulsion and microemulsion polymers tend to exhibit stability problems, e.g. polymer degradation, which appear to be exacerbated at high temperatures.
Preparing polymers in the form of dry powders addressed the above problems associated with transportation costs and disposal problems. U.S. Pat. No. 4,798,888 describes a process of making a powdered microbial polysaccharide comprising spray drying an emulsion in a non-aqueous liquid of an aqueous solution of the microbial polysaccharide. In U.S. Pat. Nos. 4,956,399; 4,956,400; 5,037,881; and 5,132,023; non-solvent precipitation and stripping are mentioned as methods of recovering dry polymer products from water-soluble polymer microemulsions. For example, U.S. Pat. No. 4,035,317, which is hereby incorporated herein by reference, teaches that water-in-oil emulsions of water-soluble polymers may be spray dried, under certain conditions, to produce free-flowing, non-dusting polymer granules which rapidly dissolve in water. Powders of polyacrylamide, acrylamide/acrylic acid copolymer, and acrylamide/dimethylaminopropyl methacrylate copolymers are described therein. However, a difficulty nevertheless remained with respect to certain functionalized polymers, and particularly with respect to those polymers that are thermosensitive. Thermosensitive polymers tended to degrade when exposed to the high temperatures encountered during the spray drying methods described in the aforesaid patents.
Attempts made to spray dry certain polymers such as, for example Mannich polyacrylamide proved to be unsuccessful. Mannich polyacrylamides were spray dried according to the teachings in the art. The resulting polymer powder exhibited reduced flocculation performance, compared to that of the corresponding polymers used in the microemulsion form. Furthermore, the viscosities of solutions of the spray dried products tended to be significantly lower than desired.
Accordingly, there exists a need for a method of recovering a functionalized water-soluble polymer from an emulsion or a microemulsion to produce a rapidly dissolving water-soluble polymer which substantially retains its flocculation performance, can be economically transported, has good thermal stability, and leads to reduced secondary pollution.
Surprisingly, a method has now been discovered for producing functionalized water-soluble emulsion and microemulsion polymers in a substantially dry form by spray drying the corresponding polymer emulsion or microemulsion. This method may be used even when the functionalized water-soluble polymer is thermosensitive. It has also been surprisingly discovered, that substantially dry polymer produced by methods of the instant invention retain the advantageous performance properties of the corresponding microemulsion product over time. Significantly, and much to the inventors surprise, the substantially dry polymers of the instant invention have greater stability than the corresponding microemulsion polymers. The processes of the instant invention also do not have problems associated with precipitation e.g. the inconvenience and cost of using large volumes of non-solvent to precipitate the polymer, the risks associated with possible flammability and toxicity of the non-solvent, the inconvenience and cost of means such as filtration to recover the precipitated polymer, etc.
In a further embodiment of the invention, the oil phase of the emulsion or microemulsion is recovered and recycled, said oil phase being surprisingly substantially free of certain polymerization-inhibiting impurities. In a still further embodiment of the invention, an acid, base, or buffer is combined with the polymer to form a granular composition with enhanced flow properties and faster rates of polymer dissolution.